1. Field of the Invention
The present invention relates to a moving -coil type (MC-type) pickup cartridge, and particularly to a pickup cartridge which generates voltage by using the leakage flux of a magnet without using any yoke.
2. Description of the Prior Art
In prior art MC type pickup cartridges, such a construction as shown in FIG. 1 is generally known. In this example, a vibrating system provided with a cantilever is oscillated within a parallel magnetic field.
In FIG. 1, a magnet 1 is prepared and, for example, two yokes 2 and 2a are attached to the both ends of the magnet 1 to form a substantially "U" shape, while a pole piece 3 is fixed to the yoke 2a at its lower end. A vibrating system 7 including a cantilever 6 with a stylus 4 fixed at its tip and an armature 5 provided thereabout at its rear is inserted into a bore 9 formed through the yoke 2 so that the armature 5 is fixed to one end of the pole piece 3 through a damper 8. Thus, the vibrating system including the armature 5 is forced to vibrate within the parallel magnetic field produced by the yoke 2 and pole piece 3 to induce an output voltage corresponding to the stylus vibration in the coil wound on the armature 5.
FIG. 2 shows another example of the prior art pickup cartridge, in which a cylindrical magnet 10 is provided in place of the magnet 1 and pole piece 3 of FIG. 1 and the vibrating system 7 is fixedly inserted through the damper 8 into a bore 12, which is formed in the magnet 10 at its one end. A front pole piece 11 is disposed in front of the coil-wound armature 5, and the cantilever 6 is inserted through a bore 13 provided in the front pole piece 11, which is in turn fixed to a cartridge body or the like, though not shown. With the pickup cartridge as mentioned above, the armature 5 is held between the yoke 2 and the pole piece 3 as shown in FIG. 1 or between the front pole piece 11 and the magnet 10 as shown in FIG. 2 so that its voltage generation efficiency is good. However, since the cantilever 6 penetrates through the bore 9 or 13 provided in the yoke 2 or the front pole piece 11, it is necessary for the cantilever 6 to have an excessive length. For this reason, there is strong possibility that the cantilever 6 will bent. To prevent such bending, the cantilever must be made thick, and hence the equivalent mass of the vibrating system is increased.
Further, when the cantilever 6 is inserted through the bore 9 or 13 of the yoke 2 or the front pole piece 11, the vibrating system 7 including the cantilever 6 is first fixed to the pole piece 3 or the magnet 10 through the damper 8 and then the yoke 2 or the front pole piece 11 is disposed. Therefore, when disposing the yoke or front pole piece, it is difficult to insert the cantilever into the bore of the yoke 2 or the front pole piece 11 through the influence of the magnet 1 or 10 so that the cantilever may be damaged during its fabrication. In addition, a signal having a large amplitude from the record disc affects the cantilever bringing it into contact with the inner wall of the bore to damage the cantilever. Further, since the armature 5 is interposed between yokes or between yoke and magnet to cause vibration within parallel magnetic field for voltage generation, the yoke or the like becomes necessary making the construction more complicated.